Battery technology, such as for electric vehicles and renewable energy applications, is an area of intense research and development. Work has focused on a number of technologies, with the most mature and successful ones being lithium-ion and lead-acid batteries. Despite this work, cost remains a central concern. Lithium ion, with its energy density, is attractive, but car-makers can pay $1,000/kW·hr or more for a lithium-ion power source. Costs remain high due to complex control and cooling systems in addition to electronics used to improve safety. This cost is at least six times the United States Advanced Battery Consortium (USABC) year 2020 target of $150/kW·hr. Contrast this with contemporary lead-acid batteries (lead-acid batteries), which can have a cost of around $150/kW·hr for renewable energy storage, but their limited energy density, cycle life, and efficiency in many cases discourages their use.